In conventional PNP transistor current mirrors, particularly those involving a plurality of outputs, the accuracy of the reflected current is a function of the Beta, or base to collector current gain, of the transistors. When the Beta is low, as is common for conventional lateral PNP transistors, the accuracy is a strong function of Beta and is therefore related to the fabrication process.
U.S. Pat. No. 4,528,496 relates to a low supply voltage capability current mirror. It teaches the well-known prior art super diode and Wilson circuits and also sets forth the formulas that describe the current mirror performance. These formulas clearly show the results of low Beta transistors.
My U.S. Pat. No. 4,546,307 also teaches the prior art super diode current mirror and sets forth some of the limitations of the circuit when using PNP transistors. The invention is directed to an NPN transistor current mirror that does not involve low Beta PNP transistors.
The above two patents are assigned to the assignee of the present invention and their combined teachings are incorporated herein by reference.